Prevalence of KIG-grades 3–5 in an orthodontic practice in North Rhine Westphalia compared with results of the DMS•6 and with KZBV data

Background and aim The prevalence of tooth and jaw malocclusions in 8- to 9-year-olds was surveyed in a nationwide setting as part of the orthodontic module of the Sixth German Study on Oral Health (DMS•6), using the orthodontic indication groups (KIG) as index. Aim of this study was the detection of the prevalence of malocclusions requiring treatment according to the KIG index in statutorily insured patients of an orthodontic practice in North Rhine Westphalia, Germany, and to compare results with corresponding DMS•6 and KZBV data. Patients and methods Between 2017–2021, n = 953 statutorily insured patients called for an initial consultation and subsequent determination of the KIG-classification and -grades. The malocclusions were classified and graded in the highest possible KIG-grade according to valid SHI guidelines. Multiple classifications were not recorded. KIG-grade > 3 according to the valid guidelines was detected in n = 815 patients. Since the DMS•6 does not contain information on KIG classifications "U" and "S", their inclusion was waived despite evaluation, leaving data from n = 683 patients for analysis and comparison. Results During the study period, n = 235 patients (34.4%) had KIG-classification "D". More than 10% were classified as "K" (120 patients, 17.6%), "P" (98 patients, 14.2%), "M" (89 patients, 13.0%), and "E" (81 patients, 11.9%). Of 16 possible classifications with KIG-grade > 3, "D4" was the most common with 26.6% (182 patients). The results confirm the findings from the multicentric DMS•6 from2021 and corresponding KZBV data from 2020. Conclusions Sagittal deviations described by classifications "D" and "M" represent with 47.4% almost half of the malocclusions with treatment need. KIG-grade D4 is the most frequent classification. There were no regional deviations of the prevalence of KIG-grades 3–5 in the district of Viersen / North Rhine compared with the national average, not even when scrutinizing a five-year-period.


Introduction
Orthodontics aim at the detection, prevention, and treatment of malformations of the masticatory system, tooth position and bite anomalies, jaw malformations and deformations of the jaws and the facial skull.The economic efficiency principle in Germany means that not all medically indicated treatments can be considered.
The assumption of costs for orthodontic treatment was restricted within the framework of the statutory health insurance (GKV;»Gesetzliche Krankenversicherung«) on 01.01.2002 by the introduction of the orthodontic indication groups (KIG;»Kieferorthopädische Indikationsguppen«) (Table 1) [1].Orthodontists must determine the patient's treatment need using KIG-classifications during the initial examination.According to current social legislation (paragraph §29 1 SGB V (»Sozialgesetzbuch« (SGB)»fünf« (V)), statutorily insured patients are only entitled to orthodontic care if they have malocclusions of a certain degree of expression or severity (KIG-grades [3][4][5], where it can be assumed that chewing, biting, speaking, or breathing is or threatens to become significantly impaired [2]. As part of the current Sixth German Study on Oral Health (DMS•6), a validated and representative epidemiological survey was conducted in the KFO-6.1 module regarding the nationwide prevalence of dental and jaw malocclusions in 8-to 9-year-olds.These results were first presented at the annual convention of the German Orthodontic Society (DGKFO) in 2022 and subsequently published in the Journal of Orofacial Orthopedics in 2023 [3][4][5][6].The primary objective of this study was to record the prevalence of malocclusions in 8-and 9-year-old children in Germany, and to derive the need for orthodontic care as a secondary objective.Data were collected between January and March 2021 in 16 locations in Germany, representative for each federal state.All relevant data were available for statistical analysis from n = 705 study participants born in 2011 and 2012 (51.4% m, 48.6% f ).The proportion of 8-year-olds was 49.4%, that of 9-year-olds 50.6%.The KIG-classifications "U" (aplasia) and "S" (eruption disorders) were not recorded in the DMS•6, as no x-rays were available.Multiple responses were possible for the remaining 9 KIG-classifications.Orthodontic treatment was indicated in n = 286 study participants according to the current guidelines of the statutory health insurance (KIG-grades 3-5), which corresponds to a rate of 40.4%.
In the DMS•6, National Association of Statutory Health Insurance Dentists (KZBV) billing data from 2020 were also published [7], including the KIG-grades 3-5 of all age groups.However, it is still unclear if these cross-section, nationwide results correspond to those of a regional population recorded long-term.

Aims of the study
The aims of this study were: 1. to determine the prevalence and severity of KIGclassifications (KIG-grades 3-5) requiring treatment in an orthodontic practice from North Rhine Westphalia, Germany, in statutorily insured patients over a five-year period between 2017 and 2021, 2. to determine the distribution of KIG-grades 3-5 among those patients, and 3. to compare the results from this five-year period with results of epidemiologic data from DMS•6 and KZBV.
Table 1 Orthodontic indication groups (KIG) according to the guidelines of the federal committee of dentists and health insurance funds for orthodontic treatment (figures in mm, "-" = not applicable)

Patient acquisition
An unselected cohort of patients with statutory health insurance was drawn from an orthodontic practice in the District of Viersen, North Rhine Westphalia, Germany.Over a five-year period between 2017 and 2021, KIG-classifications and -grades were collected and documented for n = 953 patients during their initial consultation.The period was chosen to overlap the data collection phase of the DMS•6.
Several KIG-classifications can trigger combined orthodontic treatment with orthognathic surgery in adults.Since this is a rare occurrence, only few patients aged 18 and above could be included (n=10).

Data acquisition
Tooth and jaw malposition were recorded in all possible classifications of the KIG system (Table 1).The KIGclassifications "U" (aplasia) and "S" (ectopy and retention) were recorded but not listed.Since the DMS•6 does not contain information on KIG-classifications "U" and "S", their inclusion was waived despite evaluation, leaving data from n = 683 patients for analysis and comparison.
The diagnoses were primarily obtained through clinical inspection, as required by legislation.The extent and direction of overjet, and overbite, anterior crowding and space deficits were measured intraorally using sliding calipers»Münchner Modell ® « (Dentaurum, Ispringen, Germany) with a precision of 0.25 mm.The assessment of occlusion regarding frontal and lateral crossbites was performed visually.Only if justified by clinical reasons, x-rays were made to detect possible aplasia, ectopy or retention of permanent teeth.Children and adolescents up to the age of 18 as well as adult patients who required orthognathic surgery were analysed.The classification of the data sets was carried out according to the valid framework of the guidelines of the Statutory Health Insurance (GKV) [8].This means that even if several KIG-grades > 3 were present, they were categorized exclusively according to the highest possible classification and grade.
Within the framework of the DMS•6, extrapolated billing data of the National Association of Statutory Health Insurance Dentists (KZBV) were presented as comparative figures [7].The DMS•6 thus served as an indirect source for the figures used.
For comparison with the results of the DMS•6 and the KZBV billing data, only KIG-grades requiring treatment (KIG-grades 3-5) were recorded.

Statistics
Anonymized patient data was collated using a spread sheet software (Excel ® , Microsoft Corp., Redmond, WA, USA).Normal distribution of the variable "age" was evaluated graphically and using the Shapiro-Wilk-Test with SPSS ® Version 28 for Windows ® (IBM Corp., Armonk, NY, USA).Mean and standard deviation was recorded.All other data were interpreted descriptively.

Results
Patients (Fig. 1, Table 2) N = 815 out of n = 953 statutorily insured patients required orthodontic treatment according to the applicable guidelines.As the KIG classifications "U" (aplasia, n = 46 patients) and "S" (eruption disorders, n = 86 patients) were omitted due to the methodology, n = 683 patients with an age peak at 10 and 11 years remained to be analysed.The patient age distribution is shown in Fig. 1 and Table 2.

Subdivision according to spatial plane and tooth malposition
-The prevalence of sagittal anomalies "D" and "M" is 47.4%, -The prevalence of transverse anomalies "B" and "K" is 23.6% -The prevalence of vertical anomalies "O" and "T" is 2.3%.-The prevalence of tooth malposition "E" and "P" is 26.1%.
Broken down by spatial plane and tooth malposition, sagittal deviations "D" and "M" taken together have a share of 54.4%, the transverse deviations "B" and "K" taken together have a share of 10.1%, the vertical deviations "O" and "T" taken together have a share of 16.3%, and "E" and "P" taken together have a share of 18.2%.
Broken down by spatial plane and tooth malposition, sagittal deviations "D" and "M" taken together have a Table 4 Percentage distribution of different KIG-grades requiring treatment (9 classifications and 16 grades) of the DMS•6, sample of 8-and 9-year-olds (Source: [7]  share of 52.3%, the transverse deviations "B" and "K" taken together have a share of 22.0%, the vertical deviations "O" and "T" taken together have a share of only 2.8%, and "E" and "P" taken together have a share of 22.5%.
A synoptic comparison of the present study results with those of DMS•6 and KZBV is shown in Table 6.

Limitations of the methodology
An intentional limitation of the study is that not all KIGclassifications were recorded.For better comparability, "U" and "S" were excluded from further comparison with DMS•6 and KZBV data, since they are missing in these studies.Studies from other authors show that a prevalence of approximately 5% [9] must be assumed for aplasia (classification "U") and around 6% [10] for ectopy and retention (classification "S").Within the scope of our own study, a larger proportion with KIG classification "S" (10.5%) was found, while "U" was comparable (5.6%).
A possible study limitation could be that the age of the analyzed group was not adapted to the available data of theDMS•6.No age matching subgroups were formed in the present study, as it can be assumed that the KIG distribution would have been distorted due to the preselection of patients by the regular dental practices.
Another possible limitation of the methodology could be that KIG-classifications and -grades were recorded by different examiners within one practice.According to Gesch et al. [11], there are considerable inter-examiner differences in the classification of subjects into the respective indication groups, and thus also different classifications into KIG-grades ≤ 2 and ≥ 3. Different data collection methods (clinic/dental cast) in the assessment of a malocclusion by different or orthodontically inexperienced examiners may have an unfavorable influence on examiner agreement.For this reason, KIG-classifications were made according to the four-eye principle without exception.Especially in borderline cases between KIGgrades ≤ 2 and ≥ 3, classifications were made based on a dental cast and, if necessary, a panoramic x-ray.

Comparison with available results
The DMS•6 was designed as a baseline study to provide data that will be used for an intra-cohort comparison during the DMS•7 among the same patients at a later age.The DMS•6 patients were randomly picked, while the present study used preselected patients.The selection took place in regular dental practices where malocclusions were detected to a certain degree and sent to the orthodontic specialist for further consideration.Despite the obvious inhomogeneity of the groups, the outcome was surprisingly constant.This allows the deduction that data gained so far are usable for future orthodontic caseload estimates among the German population.When comparing present results with those of the DMS•6 and the KZBV, similarities and differences become apparent.Among all studies, the sagittal classifications "D" and "M" always describe approximately half of all malocclusions requiring treatment, and the KIG-grade "D4" is the most common.However, the KIG-grade "T3" and thus the combined vertical deviations "T" and "O" occur much

Table 2 Fig. 2
Fig. 2 Percentage of the 9 different KIG-classification groups among patients with statutory health insurance in the observed period 2017-2021

Fig. 3 a
Fig. 3 a-c: Percentage of the 16 possible KIG-grades triggering treatment for patients with statutory health insurance in the observed period 2017-2021.a KIG-Grade 3. b KIG-Grade 4. c KIG-Grade 5

Table 3
Percentage distribution of different KIG-grades requiring treatment (9 classifications and 16 grades) in patients with statutory health insurance between 2017 and 2021

Table 5
[7]centage distribution of different KIG-grades requiring treatment (9 classifications and 16 grades) in the billing data of the National Association of Statutory Health Insurance Dentists (KZBV) including all age groups in the year 2020 (Source:[7]p 85, tab.3.26)

Table 6
Synoptic comparison of study results with those of DMS•6 and KZBV